This renewal project proposes to continue investigations of the following aspects of cholesterol and cholesterol ester metabolism: 1. Studies on cholesterol esterases: a. Purification of pancreatic cholesterol esterase in milligram quantities and determination of structure, mechanism of synthetic and hydrolytic activities, mechanism of bile salt activation, etc. b. Preparation of antibodies to purified cholesterol esterase for immunoassay of identity of cholesterol esterases and effects on cholesterol esterase activity and cholesterol absorption. c. Mechanism of cyclic AMP activation of hydrolytic cholesterol esterase in the adrenal cortex and other steroidogenic tissues, and evaluation of regulation of this activation as the initial control point in steroidogenesis. 2. The mechanism of cholesterol absorption, including: a. The site and activity of mucosal cholesterol esterase and related factors in the formation of cholesterol esters in the mucosa. b. Studies on the incorporation of cholesterol esters into chylomicrons and other lipoproteins in the mucosa and their transport to the lymph system. c. Role of hormones, with particular emphasis on sex hormones, on cholesterol absorption and lipid transport systems. d. Evaluation of inhibitors of cholesterol esterases on cholesterol absorption. e. Evaluation of newer anti-atherogenic compounds, with respect to direct effects on cholesterol absorption.